The present invention relates to novel chemical compounds, polymers made from such compounds and novel materials and products made from such compounds. In particular, one important use of the materials made from the invention is the manufacture of corneal contact lenses.
In recent years, corneal contact lenses have become more and more popular in the United States and throughout the world.
The great popularity of contact lenses is easily understood. One important reason is that such lenses provide perhaps the best possible manner of achieving optical correction for the eyes. The lenses fit directly over the eye, and when properly fitted, are easily retained in place. Problems common with spectacles, such as interference with peripheral vision, moving about on the head, discomfort, and the possibility of improper interpupilary distance, are easily overcome. Contact lenses provide cosmetic advantages and afford convenience and increased safety when used in diverse pursuits, particularly sporting events.
Contact lenses, which were originally made from glass, were gradually improved as improved materials became available. Now most commonly used contact lenses are generally subdivided into two types, rigid or so-called hard contact lenses, and soft contact lenses. Each type of lens has its own advantages, but each also includes certain disadvantages.
Referring first to the advantages of hard contact lenses, these lenses provide dimensional stability, so that the characteristics of an optical prescription will remain unchanged while the lens is in use on the eye. In some cases, the eye will actually conform to the contour of the lens over a period of time so as to improve the vision of the wearer. Moreover, hard contact lenses are relatively durable in relation to soft lenses.
Hard lenses may be made with small weights embedded in their peripheries, or may be cut to a prismatic shape for meridional orientation on the eye. Any lens which can be oriented, whether a hard or a soft lens, can be made into a multifocal lens, and can be cut or ground so as to have astigmatic correction, either in single vision or multifocal form.
While hard contact lenses have the above and other advantages, some patients find such lenses somewhat uncomfortable in use, and prefer the so-called soft contact lens. These lenses fall generally into three categories, namely lenses made from silicone rubber or like materials, lenses made from "HEMA" (hydroxyethylmethacrylate) or so-called "hydrogel" lenses, and finally, lenses of the methylmethacrylate base type, modified by the addition of polymers such as cellulose acetate butyrate ("CAB"). Soft lenses readily conform to the eye and are quite comfortable in short term use. They can be made extremely thin as well as soft and pliable.
In an attempt to create lenses which are permeable to oxygen and which are therefore comfortable in prolonged or extended use, both hard and soft lenses have been made which are extremely thin, some lenses being only 0.05 to 0.06 mm thick, for example. While lenses of this thickness may be worn for extended periods, they are so thin that they are very fragile and difficult to handle. Very thin lenses can be made in bifocal configurations by providing two or more different radii of curvature on the front surface. Thicker lenses may be truncated at the bottom and/or made prismatic so that they will orient themselves on the eye. However, while theoretically attractive, lenses of this sort have been successful in actual use only occasionally, and thus are not in widespread use.
Referring now to HEMA type lenses, while these lenses possess reasonable dimensional stability, they sometimes absorb water, and hence expand, somewhat unevenly, thus assuming a distorted shape and causing slight visual distortion for the user. Thus, while HEMA lenses are reasonably satisfactory, their dimensional stability is not as good as that of hard contact lenses.
At present, there is another "trade-off" in relation to lenses intended for prolonged or extended use. Thus, when lenses are thin enough to be sufficiently permeable for comfort, they may be too delicate to be cleaned frequently, but on the other hand, if they are not cleaned frequently, proteinaceous and other deposits from the eye may form a coating on the lens which interferes with clear vision.
In view of the foregoing advantages of contact lenses, it would be even further advantageous if there were a hard contact lens material that possessed the known advantages of machinability, dimensional stability, toughness and optical clarity, and which were also sufficiently oxygen-permeable in relatively greater thicknesses to be worn by a user for an extended period, such as for several days, weeks, or even months or more. Hard contact lenses which could be worn for an extended period would eliminate common problems both with existing hard and soft type lenses. These problems include losing or misplacing the lenses because of frequent handling, contamination, and wear and tear occasioned by such handling, and the general inconvenience of locating and inserting the lenses when they are needed but not being worn.
Referring to handling, it is not uncommon for a pair of hydrogel lenses costing perhaps hundreds of dollars, to last for only about one year or so without cracking or becoming torn as a result of frequent handling. More sturdy lenses, such as known types of hard lenses, are not susceptible to tearing or cracking, but can be scratched by frequent removal and insertion, and cleaning, particularly if they are dropped occasionally. Losing the lenses is a realistic possibility which could be minimized substantially by having lenses which are removed weekly, or monthly, or at greater intervals.
An improved oxygen-permeable hard contact lens which could be made in moderate thicknesses could be reasonably rugged and could provide freedom from bacterial penetration, and realize the potential of hard lenses for shape retention and optical correction while on the eye.
Referring now to prior attempts to provide polymers with increased oxygen permeability, normally, most or all such known polymers have either been too dimensionally unstable for satisfactory use, or have had other disadvantages. For example, it is known to add significant amounts of additives normally intended to increase wettability. While such materials are helpful in proper amounts, using excess amounts thereof has often tended to cause proteinaceous matter to deposit on and impair the transparency of the inner surface of the lens. This has been a particular problem with middle aged and older persons, who often use multifocal lenses which are inherently relatively thick in relation to single vision lenses.
While numerous attempts have been made to improve the oxygen permeability of both hard and soft contact lenses, the attempts have met with only limited success, particularly in thicker lenses. Moreover, many soft lens materials provide an environment which is highly suitable for bacterial growth, and this calls for sterilization procedures which in turn require the lenses to be handled frequently.
The present invention, therefore, is intended, from the standpoint of an end use product, to provide contact lens materials which are sufficiently oxygen permeable that they may be worn by the user on a greatly extended basis in relation to prior art lenses, which do not have the disadvantages associated with known prior art lenses intended for this purpose.
Referring now to its chemical aspects, the invention relates to the manufacture of copolymers of an acrylic or methacrylic material of a known type, and novel, silicone-substituted acrylic and methacrylic compounds so as to produce an oxygen-permeable plastic material which is uniquely suitable for manufacturing novel corneal contact lenses as referred to above. The expression "copolymers" is sometimes used herein for simplicity in referring to a polymer which includes two principal comonomers, although such polymer may incidentally include one or more additional, known monomers in minor amounts, for purposes such as cross-linking, increasing the wettability of the final product, or otherwise.
The copolymer compositions, and products made therefrom, are improved over counterpart prior art compositions by reason of increased dimensional stability and improved gas permeability. Such novel compositions also retain or provide improvements in desirable prior art characteristics such as optical clarity, the ability to be cast, molded, or machined, and compatability with chemically bonded, hydrophilic materials adapted to improve the wettability of the finished product.
Preferably, the compositions comprise high molecular weight polysiloxanylalkyl esters of acrylic and methacrylic acids and other compositions as monomers, copolymerized with methacrylates or other esters of acrylic or methacrylic acids.
According to the invention, one comonomer (the "first" comonomer) is an acrylic or methacrylic ester silane, substituted with one or more highly substituted siloxanyl groups. One such typical first comonomer is a tris-trimethylsiloxysiloxanyl methacryloxyalkylsilane, which can be copolymerized with an alkyl acrylate or alkylmethacrylate, (the "second" comonomer), with this copolymer composition in turn being cross-linked to a slight degree by cross-linking monomers, and preferably further modified by the addition of small amounts of compounds intended to increase the wetability of the finished copolymer material. This basic polymerization of the novel comonomers with known comonomers occurs through a known double-bond polymerization mechanism.
A still further facet of the invention includes synthesis of a branched comonomer which includes tris-trmethylsiloxysiloxanyl groups. One, two, or three such groups are bonded to a silicon atom of an alkyl silane ester of acrylic or methacrylic acid.
A certain proportion, such as 10% to 60% of this compound, is then polymerized with one or more or other second comonomer compounds having the same or similar acrylic or methacrylic ester portion, together with the minor amounts of cross linking and wetting agents, referred to above.
One more aspect of the present invention relates to the method of making the so-called first or novel comonomers of the invention. According to this method, methylethersilanes are reacted with acetoxy derivatives of polysiloxanyl groups, using aqueous ethanoic sulfuric acid as a catalyst. The details of this method are brought out in other portions of the specification. In still another aspect, the invention relates to alternate methods of preparing the above or similar products. One alternate method comprises reacting trichloroalkylmethacrylates with an excess of pyridine and reacting the resulting intermediates with polysilanol compounds at about -50.degree. C.
Monomer is removed from these reaction mixtures by purification following removal of the low molecular weight materials, with the reaction products being purified by washing with weak alkalies, or like materials.
A typical novel comonomer compound of the present invention can be represented by the following general formula: ##STR1## wherein R is selected from the class consisting of lower alkyl groups and hydrogen, and n is an integer from about one to three, wherein X and Y are selected from the class consisting of lower alkyl groups, cycloalkyl groups, phenyl groups (substituted or unsubstituted), polysiloxanyl groups, fluorine and Z groups; Z is a group of the structure: ##STR2## and wherein A is selected from the class consisting of lower alkyl groups and phenyl groups.
In the alkyl or phenyl ester second principal comonomer, the alkyl group contains 1 to about 20 carbon atoms, (typically one to six carbon atoms) and the phenyl ester contains a singly phenyl group.
One compound which may be used as the first principal comonomer of the present invention is a tris-trimethylsiloxysiloxanylalkyl ester comonomer such as: ##STR3## n is an integer from about one to three
Another compound is: ##STR4## wherein n is an integer from about one to three.
Still another compound is: ##STR5## wherein n is an integer from about one to three.
Another suitable compound is: ##STR6## wherein n is an integer from about one to three.
Still another compound is: ##STR7## wherein n is an integer from about one to three.
One more suitable compound is: ##STR8## wherein n is an integer from about one to three.
Representative known or second comonomers which may be employed in the practice of the invention include the following:
methyl acrylate and methacrylate PA0 ethyl acrylate and methacrylate PA0 propyl acrylate and methacrylate PA0 isopropyl acrylate and methacrylate PA0 butyl acrylate and methacrylate PA0 hexyl acrylate and methacrylate PA0 heptyl acrylate and methacrylate PA0 octyl acrylate and methacrylate PA0 2-ethylhexyl acrylate and methacrylate PA0 nonyl acrylate and methacrylate PA0 decyl acrylate and methacrylate PA0 undecyl acrylate and methacrylate PA0 lauryl acrylate and methacrylate PA0 cetyl acrylate and methacrylate PA0 octadecyl acrylate and methacrylate PA0 cyclohexyl acrylate and methacrylate PA0 benzyl acrylate and methacrylate PA0 phenyl acrylate and methacrylate PA0 ethyleneglycoldimethacrylate PA0 diethyleneglycoldimethacrylate PA0 triethyleneglycoldimethacrylate PA0 tetraethyleneglycoldimethacrylate PA0 polyethyleneglycoldimethacrylate PA0 acrylic acid PA0 methacrylic acid PA0 N-vinyl 2-pyrrolidone, and
Cross-linking monomers include difunctional compounds such as:
and other compounds known to those skilled in the art for use in cross-linking compounds of the type referred to herein.
The wetting agents include, but are not limited to:
hydroxyalkyl esters of acrylic and methacrylic acids.
Referring now to the compounds referred to above, and used as intermediates to make more highly branched "tris" compounds, one such compound, for example, is tristrimethylsiloxy-silane which is manufactured by a low temperature method. Typically, the method consists of treating one mole of trichlorosilane in a suitable anhydrous solvent with about a three molar excess of pyridine at (-50.degree. C.), and then treating the resulting intermediate product with a three equimolar amount of trimethylsilanol, which is also in a suitable anhydrous solvent, while the entire reaction mixture is maintained at about -50.degree. C. After all products are added, the mixture is brought rapidly to room temperature. From this, tris-trimethylsiloxy-silane may be removed by fractional distillation.
A still further aspect of the invention relates to the preparation of tris(trimethylsiloxy)acetoxysilane, and to a method of making such compound. The details of the manufacturing method are set out in the specification hereof; this compound is a useful intermediate in the preparation of the comonomers used as described herein.
In view of the shortcomings of prior art contact lenses and the compounds and compositions used in making them, it is an object of the present invention to provide novel monomers useful in making improved lens materials, improved polymer compositions made from such novel monomers, and improved lenses made from such polymers.
Another object of the invention is to provide novel silicone compounds used as components of polymerizable monomers.
A still further object is to provide a method of making starting or intermediate materials for making novel silicione compounds, and to provide starting and intermediate materials for other uses as well.
Yet another object is to provide highly branched or substituted silane, silanol and siloxane materials for a variety of uses, including the manufacture of copolymers, terpolymers or other polymers incorporating such materials.
Another, more specific, object is to provide a novel method of making pentamethyldisiloxane.
A still further object is to provide one or more compounds containing alkyl esters of acrylic or methacrylic acids, and incorporating one, two, or three tris(trimethylsiloxy)siloxanyl groups.
A still further object is to provide an optically useful, novel polymeric material of increased oxygen permeability with respect to prior art compounds.
Still another object is to provide a material of the foregoing type which may be formulated or synthesized so as to have a desirably high refractive index, and which can therefore be used in the manufacture of bifocal contact lenses, particularly fused bifocal contact lenses.
A still further object is to provide a composition which will make possible the manufacture of corneal contact lenses which can be worn for an extended time period while providing greatly increased comfort to the wearer.
Another object is to provide a polymeric contact lens material which is compatible with additives of known kinds used to provide other desirable end use properties.
A further object is to provide an oxygen-permeable polymer which has non-optical uses, such as forming membranes or containers for blood or other dialyzable material which can be purified by absorption of oxygen and/or transpiration or loss of other gaseous components, and for making apparatus for transferring blood or other material to and from, and through dialysis machines, for example.
A still further object is to provide a method of manufacturing copolymers incorporating the compositions made by the novel methods referred to above.
These and other objects and advantages of the invention, including those inherent therein, may be achieved in practice by carrying out the methods, and making the compounds and compositions referred to herein. The following examples, which are set forth by way of illustration and not by way of limitation, illustrate preferred methods of carrying the invention into practice.